1. Field of the Invention
The present invention relates to a method for producing ε-caprolactam from cyclohexanone oxime, the ε-caprolactam being useful as a raw material for producing nylon 6. More particularly, the present invention is concerned with a method for producing ε-caprolactam from cyclohexanone oxime, wherein the method includes the following first or second aspect: in the first aspect, the method comprises contacting cyclohexanone oxime with a specific solid acid catalyst in the gaseous phase to effect a rearrangement reaction of the cyclohexanone oxime, to thereby produce ε-caprolactam; or in the second aspect, the method comprises contacting cyclohexanone oxime with a solid acid catalyst in the gaseous phase to effect a rearrangement reaction of the cyclohexanone oxime, wherein the rearrangement reaction is effected in the presence of a specific polyhydric alcohol compound, to thereby produce ε-caprolactam.
The method of the present invention is advantageous not only in that ε-caprolactam can be produced with high selectivity and in high yield, but also in that the catalyst used in the method of the present invention can be shaped into a practical morphology useful in a commercial process, and also has excellent mechanical strength, so that the catalyst can be used for various catalytic reaction processes, such as those processes using a fixed-bed reactor, a fluidized-bed reactor and a moving-bed reactor; and the catalyst can also be used for a reaction process which is performed for a long time while frequently repeating a cycle of reaction and catalyst regeneration. Therefore, the method of the present invention is advantageous for producing ε-caprolactam stably for a long time.
2. Prior Art
ε-Caprolactam is known as an extremely important key chemical material for use in producing various chemical products, such as nylon 6. At present, commercial production of ε-caprolactam is mainly performed using a method which comprises contacting cyclohexanone oxime with an oleum catalyst (i.e., fuming sulfuric acid) in the liquid phase to effect a rearrangement reaction of the cyclohexanone oxime, to thereby produce ε-caprolactam. However, this method poses problems in that a large amount of ammonium sulfate is generated as a by-product, and that the reaction apparatus is corroded by the oleum. These problems have not yet been solved.
On the other hand, with respect to a method for producing ε-caprolactam, which comprises contacting cyclohexanone oxime with a solid acid catalyst in the gaseous phase, there have been a large number of proposals.
Unexamined Japanese Patent Application Laid-Open Specification No. Sho 57-139062 (corresponding to U.S. Pat. No. 4,359,421) discloses a method for producing ε-caprolactam by using a zeolite as the solid acid catalyst, wherein the zeolite has a silica/alumina ratio of 12 or more and a constraint index in the range of from 1 to 12, namely the zeolite is any of ZSM-5 zeolite and other specific ZSM zeolites.
Unexamined Japanese Patent Application Laid-Open Specification No. Sho 62-123167 (corresponding to U.S. Pat. No. 4,709,024) discloses a method for producing ε-caprolactam by using a crystalline zeolite catalyst which has a constraint index in the range of from 1 to 12, and which has an Si/Al atomic ratio of 500 or more and an external acid amount (the number of acidic sites observed on the crystal surface) of 5μ equivalent/g or less.
However, all of these methods have a common disadvantage caused by the sole use of the zeolite (which is the active species) as a catalyst.
In the commercial scale practice of a gaseous phase reaction process using a zeolite catalyst, it is very seldom to use a zeolite alone as a catalyst. Rather, in most cases, a zeolite is used in the form of a shaped article having an appropriate morphology, which is obtained by shaping a mixture of a zeolite with a conventional binder, such as a silica, a silica-alumina, or an alumina. This is because a zeolite is polycrystalline and, hence, is very difficult to shape into a desired morphology.
However, when a rearrangement reaction of cyclohexanone oxime for producing ε-caprolactam is performed using the above-mentioned zeolite in the form of a shaped article obtained by shaping a mixture of the zeolite with a conventional binder, such as a silica, a silica-alumina, or an alumina, there arises a problem in that, since those conventional binders are not inert to a reaction system for the above rearrangement reaction, the binders promote side reactions (e.g., reactions to by-produce a tar and a pitch), thus disadvantageously shortening the life of the catalyst and markedly reducing the catalytic activity and the selectivity for ε-caprolactam.
In an attempt to solve this problem, Unexamined Japanese Patent Application Laid-Open Specification No. 2000-202296 (corresponding to EP 1 002 577 A1) proposes a process for producing a catalyst which comprises an MFI zeolite and a siliceous ligand as main components, and which is suitable for use in a rearrangement reaction to convert an oxime into a corresponding amide. Specifically, the process proposed in this patent document comprises bonding the submicronic zeolite particles to a ligand obtained by acid hydrolysis (i.e., hydrolysis effected in an acidic solution) of a silicon alkoxide. However, this process has a disadvantage in that the catalyst production needs to be conducted while strictly controlling the production conditions, such as pH value and degree of dispersion of the zeolite, thus rendering complicated the production process.
Japanese Patent No. 3023581 (corresponding to U.S. Pat. No. 5,407,881) discloses a method using as a catalyst a zeolite shaped article having its strength improved by a treatment in which a pentasil type zeolite shaped article obtained without using any inorganic binder is contacted with an alkaline solution having a pH value in the range of from 9 to 13, at 30 to 100° C. However, when such a catalyst containing no inorganic binder as described above is used for a long time, the catalyst is likely to become powdery during the reaction due to the unsatisfactory mechanical strength of the catalyst. This method has also a disadvantage in that, when the catalyst containing no inorganic binder is subjected to further treatment for improving the strength of the catalyst, the production process becomes cumbersome.
Apart from the above-mentioned methods, there have also been disclosed methods for producing ε-caprolactam in the gaseous phase, in which the rearrangement reaction is effected in the copresence of a zeolite as a catalyst and a specific compound.
For example, EP 0 380 364 A2 discloses a method in which a gaseous phase reaction to produce ε-caprolactam from cyclohexanone oxime is effected in the copresence of a solid acid catalyst and a compound represented by the following formula: R1—O—R2 (wherein R1 represents a lower alkyl group which may be substituted with a fluorine atom, and R2 represents a hydrogen atom, a lower alkyl group or a phenyl group). That is, in this method, the reaction to produce ε-caprolactam is effected in the copresence of a solid acid catalyst and an ether compound or a lower alcohol.
Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 10-87611 describes a method for producing ε-caprolactam, which comprises contacting cyclohexanone oxime with a catalyst selected from the group consisting of a ZSM-5 zeolite having an Si/Al atomic ratio of less than 100, a mordenite zeolite and a Y type zeolite, in the gaseous phase in the presence of an aliphatic alcohol having seven or more carbon atoms.
However, with respect to the above-mentioned patent documents which describe the use of a specific compound in combination with a zeolite, all of these patent documents use a zeolite alone as a catalyst and have no description about the use of a catalyst in the form of a practically useful shaped article obtained by shaping a zeolite using an appropriate binder.
Further, in practicing the production of ε-caprolactam by the rearrangement reaction of cyclohexanone oxime, in most cases, a carrier gas is used, for facilitating the contact between the raw material and the catalyst. In the actual process, it is necessary to separate the carrier gas used in the reaction from the above-described specific compound (such as an ether compound and/or a lower alcohol) used in combination with a zeolite.
However, when an ether compound and/or a lower alcohol are/is used, there arises a problem in that such compounds generally have a low boiling point, so that it is difficult to separate the carrier gas from the compounds.
On the other hand, when a higher alcohol is used, there arises a problem in that a higher alcohol generally has too high a boiling point which is close to the boiling point of cyclohexanone oxime, so that it is difficult to separate the cyclohexanone oxime from the higher alcohol.